Polypropylene-based resins excellent in recycling properties are used in components of the air intake system of the conventional internal combustion engine. To reinforce the strength or rigidity of the components of the air intake system of an internal combustion engine at high temperatures or to minimize leakage of noises generated inside the air intake system at the time of air intake, specifically to improve inertance (inertance is indicative of difficulty of transmission of wave motion inside a component), an inorganic filler such as talc is added to the polypropylene-based resin. By increasing the amount of the inorganic filler, the above-mentioned properties can be improved (see Patent Document 1, for example)
When a significantly large amount of filler is used, problems such as lowered flow processability at the time of molding and insufficient filling arise.
Recent technologies require automobiles to be manufactured using materials which are light in weight. Therefore, an increased amount of filler cannot be used in components of the air intake system, since the weight of the components eventually increases due to the high specific gravity of the filler.
From the viewpoint of thermal recycling (recovery of energy generated by combustion), a need has been felt for a technology for reducing the amount of combustion residues. Taking this point into consideration, the amount of inorganic filler cannot be increased.
Use of glass fiber having a larger aspect ratio than that of ordinarily used talc provides a better rigidity improving effect for a smaller amount of inclusion. However, use of such a fibrous filler causes warping deformation of the component during molding. Therefore, use of a small amount of mica, which is a sheet-like filler, has been proposed to suppress the occurrence of warping deformation and to obtain rigidity equivalent to or larger than that obtained using glass fibers.
To decrease the amount of combustion residues, graphite powder or carbon fiber is used as the filler. Graphite is used alone as the filler (Patent Document 2, for example). Components obtained using graphite alone exhibit insufficient strength. If a carbon fiber is used alone as the filler, the resultant components undergo warping deformation during molding. Therefore, a proper amount of an inorganic component such as mica is mixed in.
Although teachings are found regarding specific. improvement of internal loss by use of a carbon filler (Patent Document 3, for example), the relationship between the apparent density of graphite and resonance frequency has not been elucidated.
Patent Document 1: JP-A-2005-023164
Patent Document 2: JP-A-01-319549
Patent Document 3: JP-A-02-058552
As explained above, there has been a desire for a resin which is based on polypropylene excellent in recycling properties, can suppress occurrence of warping deformation without increasing the amount of combustion residues while maintaining a high degree of strength and rigidity, and can improve acoustic properties as compared with inorganic filler-containing resins.
An object of the invention is to provide a resin composition for a component of an air intake system of an internal combustion engine which can improve acoustic properties while maintaining high strength and low specific gravity and generates a reduced amount of combustion residues, as well as a component of an air intake system using the resin composition.